Is there any software that converts latex file to tex file?

Question

I was asked to convert a file from LaTeX format to TeX format, so it could be compiled by TeX. I use LaTeX a lot, but I'm quite unfamiliar with TeX. And the file is pretty long. So I was wondering if there's software or trick could simplify a bit the task.

BTW, I haven't installed TeX on my Ubuntu machine because I think I can use pdftex to test if the file is compatible with TeX. Am I right?

---

Edit:

The reason that I need to do this is that my supervisor asked me to convert something that I wrote with LaTeX into TeX style because he only knows how to use TeX. So the file should not only be compiled by TeX, but the grammar should also be TeX style so my supervisor could understand and modify it.

Answer 1

Adding

\def\patterns#1{}
\catcode`\{=12
\let\newtoks\relax
\let\dump\relax
\let\+\relax
\let\newinsert\relax

% extra lines for 2019 latex release
\let\newmarks\relax

\let\acute\relax
\let\grave\relax
\let\ddot\relax
\let\tilde\relax
\let\bar\relax
\let\breve\relax
\let\check\relax
\let\hat\relax
\let\vec\relax
\let\dot\relax
\let\widetilde\relax
\let\widehat\relax

% end of addition

\input latex.ltx

To a LaTeX file makes it a plain TeX file.

This is a LaTeX answer I gave to a question earlier today which runs without error in pdftex as modified:

\def\patterns#1{}
\catcode`\{=12
\let\newtoks\relax
\let\dump\relax
\let\+\relax
\let\newinsert\relax
\let\newmarks\relax

\let\acute\relax
\let\grave\relax
\let\ddot\relax
\let\tilde\relax
\let\bar\relax
\let\breve\relax
\let\check\relax
\let\hat\relax
\let\vec\relax
\let\dot\relax
\let\widetilde\relax
\let\widehat\relax

\input latex.ltx
\documentclass[a4paper]{IEEEtran}

%\usepackage[ngerman]{babel}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{lipsum,tabularx}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Here, main documents begins %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}

\title{FooBar}
\author{Bar Foo,~\IEEEmembership{[email protected]}}

% The paper headers
\markboth{FooBar 2013}%
{FooBar2013}

% make the title area
\maketitle

%% -----------------
%% |   Main part   |
%% -----------------

\lipsum

\section{aaa}
\noindent
\begin{tabularx}{\linewidth}{@{} r X @{}}
    Step 1: & \lipsum[1] \\
    Step 2: & \lipsum[2] \\
    Step 3 ggggggg kk kk jj gg : & \lipsum[3] \\
\end{tabularx}

\makeatletter
\renewcommand*\@IEEEiedmakelabel[1]{\hspace\labelsep
                                \parbox[t][0pt][t]{\itemindent}{\raggedright\normalfont\bfseries #1}}
\makeatother
\section{bbb}

\begin{description}

\item[Step 1]
 \lipsum[1]
\item[Step 2]
\lipsum[2]
\item[Step 3 ggggggg kk kk jj gg ]
\lipsum[3]
\end{description}


\makeatletter
\renewcommand*\@IEEEiedmakelabel[1]{\hspace\labelsep
                                \makebox[\linewidth][l]{{\normalfont\bfseries #1}}}
\makeatother
\section{bbb}

\begin{description}

\item[Step 1]
 \lipsum[1]
\item[Step 2]
\lipsum[2]
\item[Step 3 ggggggg kk kk jj gg ]
\lipsum[3]
\end{description}


\end{document}

Answer 2

»So the file should not only be compiled by TeX, but the grammar should also be TeX style so my supervisor could understand and modify it.«

I'd be very surprised to see a full solution to this problem. One thing is that TeX can compile a file, but it is a completely other thing to convert LaTeX into readable TeX, which can be handled, revised, changed, amended, in short: be a basis for further writing.

Just as an example: 

The line \documentclass[pagesize, parskip=half, headings=big, english, DIV=calc, BCOR=5mm]{scrartcl} contains quite a lot of instructions. How in the world transfer this into plain TeX except including more or less the whole KOMA-script bundle into the file?

Maybe you tell us a bit more about your file and the intentions of your supervisor.